1. Field of the Invention
This invention relates to HEPA or high efficiency particulate air filters of the laminar flow type, and more particularly to improvements thereof which comprise integral separators between folded filter panels.
2. Description of the Prior Art
High efficiency particulate air filers or HEPA filters as known today, have been on the market for approximately thirty years, and are extensively used in major industries, including the atomic, semi-conductor, space, chemical and pharmaceutical industries, and for health care including operating rooms and other clean air facilities. These filters generally consist of a pleated fiber glass element cemented into a frame, and with the pleats separated for free air passage by separators.
It has heretofore been proposed to provide various types of interposed separators between filter elements which are made of corrugated aluminum, kraft paper or synthetic plastic materials.
It has also heretofore been proposed to provide dimples to serve as separators.
It has also been proposed to corrugate the entire filter media and then fold the material back and forth across the corrugations.
It has also been proposed to provide a plurality of geometrical configurations to provide separation but none of these provide laminar or turbulence free air flow.
British Pat. No. 798,765 in FIG. 1 discloses a panel which is expressly stated as not requiring separate spacers between the filter sheets to hold them apart. As shown in FIG. 1, the filter strip has a checkerboard appearance with spacers formed integrally with the filter sheets themselves so that when the strip is folded the corrugations engage flat surfaces to retain the separations but do not produce laminar or turbulence free air flow.
Czerwonka, in U.S. Pat. No. 3,280,985 discloses a fluid filter arrangement, wherein the filter media includes alternating finer and more porous filter medium positioned in coextending faced relationship, and separated by ribs, as a unit in pleat form, to extend across a dirty gas stream to be treated. No alternating filter arrangement like my invention is disclosed in Czerwonka nor would it produce a laminar or turbulence free air flow.
Czerwonka, in U.S. Pat. No. 3,386,227 discloses an electrostatic filter device in which the filter sheets 7 are of porous, dielectric materials and with separator sheets of electrically conductive material, but which also does not provide a laminar or turbulence free air flow, nor can it be used for clean rooms and in clean air equipment.
Hart, in U.S. Pat. No. 3,410,062 discloses a filter wherein the filter media is composed of a stack of panels with each panel provided with V corrugations, which provide extra filter area and space the panels.
No structure similar to my invention is disclosed, and which provides for laminar and turbulence free air flow through the filter.
Hart, in U.S. Pat. No. 3,531,920 discloses a filter which has a core composed of a zig-zag series of self-sustaining planar panels, connected by alternate upstream and downstream folds, with the folds spaced to provide V shaped pockets for the air to enter and V shaped pockets for filtered air to leave.
No structure similar to my invention is disclosed in Hart, and which provides for laminar and turbulence free air flow.
Buckman et al., in U.S. Pat. No. 3,799,354 discloses a filter element, which is formed from a strip of sheet filter material folded in zig-zag fashion about a center tube, with alternate pleats so as to provide a larger area of filter paper in the same space as a conventional star form filter element. No structure is disclosed in Buckman et al. which provides for laminar or turbulence free air flow. In addition, the Buckman et al. structure discloses a hollow tubular filter which is suitable for special purposes and not designed for use with clean rooms or clean room equipment.
Hladik, in U.S. Pat. No. 4,199,387 discloses a method of cementing filter media to a frame for high temperature applications, but does not provide a structure with the characteristics of my invention or that provides for laminar or turbulence free air flow.
The French Pat. No. 745,466 discloses the joining of individual panels A using channels C, which does not provide an integral structure nor one with laminar or turbulence free air flow.
The HEPA filter of my invention can be fabricated from a continuous strip of filter material with integral separators, which avoids the problems of previous structures while permitting the use of a larger sheet of filtering material thus increasing the overall filtering surface, thereby allowing for a higher volume of air to flow through the filter at a relatively lower pressure drop, with laminar and turbulence free air flow.